Thursday, June 18, 2009

Yesterday's meeting with the textbook rep clarified several tasks (listed below in no particular order):

1. The textbook publisher could create a composite textbook for us, made up of chapters taken from two or more different sources. But this may be more suitable for a survey course than for one that gradually builds expertise The rep will find out whether instructors have used 'composite' textbooks for courses like ours, and if so will put us in touch with the instructors.

2. The textbook rep will find out about on-line genetics activities provided to students with the various textbooks. And we will go through the activities she discovered in one of the textbooks, to find out how suitable they would be for our students (we want interactive activities, where students have to make decisions about what to do and predictions about what will happen).

3. I will dig out our old autotutorial genetics material to see if some of that could be repurposed for this new course.

4. We will look more carefully at the available textbooks, to determine what might be suitable. In particular, is there a textbook that would be OK if it were supplemented with one or two chapters from other sources, or with a week or two of material we have written specifically for our course?

5. We will prepare an email to the authors of existing genetics textbooks, explaining the approach we want to take and asking if they know of any suitable textbooks or other resources. (We'll also give this to the rep.) Here's a draft for us to start with:

Dear genetics textbook author,

We are planning a new genetics course for second-year biology majors, but we haven't been able to find any textbook that uses the approach we think best (described below). So we're contacting the authors of respected genetics textbooks to ask if they might know of something suitable.

After many years of teaching genetics, we feel that understanding the core of genetics has three main components. First, students must understand meiosis and its genetic consequences - how parental genotypes give rise to gamete genotypes, and how random gamete fusion creates offspring with new combinations of parental genotypes. Second, students must understand how genotypes produce phenotypes - how genes and proteins work, the role of environmental variation, how changes to DNA sequences change gene activities, and how, in diploid organisms, different alleles of the same or different genes interact to produce phenotypes. (This last point is perhaps the most important: students need to understand the molecular basis of dominance and epistasis.) Finally, once students have some mastery of both inheritance and phenotypes, they must learn to put these together to understand how phenotypes are inherited.

We have been unable to find any textbook that takes this approach. Traditional (Mendel-first) texts throw students in at the deep end, asking them to start applying Mendelian principles without any explanation of their causes. Even the simplest Punnett square implicitly requires students to figure out parental genotypes from parental phenotypes, to predict the gamete genotypes and proportions these parents will produce, to predict the offspring genotypes and proportions that random fusion of these gametes will produce, and to predict the offspring phenotypes from these genotypes. It's not surprising that students cope by blindly memorizing rules and patterns. Later chapters in the textbooks do teach meiosis and gene action, but most students treat these explanations as independent facts to be memorized, and never really make the causal connections between them and the rules and patterns they began with. (If you doubt this, try asking students why we see dominance.)

DNA-first textbooks give students all the facts of molecular biology before introducing Mendel, but students are unable to use this information to predict phenotypes because the text spent no more than a paragraph on the critical issue of what happens when two different alleles are present. And meiosis is again treated largely as patterns to be recognized, with no emphasis on using it to predict gamete genotypes.

Here's what we think is missing from the textbooks we've examined:

Material that teaches students to predict gamete genotypes from parental genotypes. This needn't be a chapter in itself, but the basics should be introduced when meiosis is introduced, and extended when each new complication is brought up. For example, when crossing over or chromosome rearrangements are taught, students should also be taught how to predict the gamete genotypes that crossovers and rearrangements will produce. This teaching needs to be accompanied by appropriate problems. For example: "A man has genotype a1 a2 b1 b2. What gametes will a single meiosis produce? What gamete genotypes will the pooled products of many meioses contain, and in what proportions?"

Material (probably a chapter) that teaches students about the causal relationships between diploid genotypes and diploid phenotypes, explicitly incorporating the molecular basis of each effect. (Haploids could also be in such a chapter.) What if one allele produces a functional enzyme but the other produces no enzyme at all? What if one allele of a repressor gene is defective?

We really don't want to write our own textbook, or even our own supplementary chapters. Might you know of any textbook that takes the approach we're looking for. Or perhaps just a chapter or other written material that could fill in the gaps we see?

Wednesday, June 17, 2009

The Genetics planning committee (or whatever we are) is about to meet with a textbook rep to discuss options for getting a textbook that fits the kind of course we want to teach.

I'll set aside for now the issue of whether we want a textbook at all. I think we need a set of required readings (and maybe activities) that we expect students to complete BEFORE they come to class. These could be chapters of a standard textbook, a collection of chapters from different textbooks that a publisher has put together for us, stuff we wrote ourselves, or ???

Why a typical genetics textbook isn't suitable:

Our approach to teaching genetics seems very sensible to us, but it's certainly not the one most courses take. Genetics courses and textbooks usually start either with some combination of Mendel's discoveries, meiosis and DNA/gene expression, introducing the basics of what's called 'transmission genetics'. They may do Mendel first, or DNA first. Students learn to predict phenotypes of offspring from phenotypes of parents, and vice versa. To do this they need to have memorized 'Mendel's laws'. In this context our current understanding of molecular biology and meiosis is presented as explaining what Mendel found.

We instead want to separately teach the two components of transmission genetics. We will thoroughly teach how DNA sequences determine phenotype, building a solid molecular foundation for such concepts as ploidy and dominance. Separately we'll teach how DNA sequences are inherited (meiosis, gamete fusion, chromosome reassortment and crossing over, etc.). Only once both components have been solidly established will we combine them to teach about the inheritance of phenotypes.

But we can't find a textbook that does a proper job of teaching how genotype determines phenotype. This deserves at least one full chapter, maybe more, but textbooks usually gloss over it, assuming that students who understand how DNA makes RNA makes proteins and what proteins do will automatically grasp the implications for phenotypes, especially in diploids.

So maybe the solution is to use a standard textbook but somehow create this anomalous chapter ourselves, or find it somewhere outside of the usual textbooks.